Let’s get one thing out of the way: nothing’s truly original anymore; it’s the same thing with a little something different. Even if you find what you think is an entirely new creature in the Fantasy book you just finished, someone else will point out at least one other creature that is very similar.
With that said, authors still try to give readers something new(-ish) and readers often rant how they want to find a book with something unique in it. However, sometimes it’s these same people that would complain that there are too many new (unfamiliar and original as they could be) things in a book and that they (the readers) can’t keep up with all of them.
People find comfort in familiarity and even those who claim they want something really, really original seek that with which they are acquainted. What we as writers must do is try to find a balance and add both familiar and original elements to our stories. That way our readers would be excited about the original bits, but not overwhelmed because there is something familiar as well.